Display device and method

ABSTRACT

According to one embodiment, a display device includes a display panel, a light source, a light guide and a prism sheet. The display panel includes a display area in which unit pixels each containing first sub-pixels and second sub-pixels are arranged along a first direction and a second direction. In the display area, the first sub-pixels have a width different from that of the second sub-pixel in at least one of the first direction and the second direction, or each unit pixel contains different numbers of first sub-pixels and second sub-pixels. The prism sheet is interposed between the light guide and the display panel and includes prisms extending along a third direction inclined with respect to the second direction by an acute angle of inclination.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-112476, filed May 30, 2014, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a display device and amethod of suppressing moirés.

BACKGROUND

Display devices such as liquid crystal display devices comprise adisplay panel including a display area in which unit pixels comprising aplurality of types of subpixels corresponding to respective differentcolors are arranged in matrix, and a prism sheet interposed between thedisplay panel and the light source.

The prism sheet comprises, for example, linearly extending prismsarranged parallel to each other at a predetermined pitch. When lightfrom the light source passes through the prism sheet, the light isconcentrated in a predetermined range by each of the prisms to createshades corresponding to the prisms, respectively. These shades sometimesinterfere with the subpixels in the display area to create the so-calledmoiré on the screen of the liquid crystal display device.

An object of an embodiment disclosed here is to suppress moiré caused bysubpixels of a display area and a prism sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view schematically showing an example of thestructure of a liquid crystal display device.

FIG. 2 is a cross sectional view schematically showing an example of thestructure of a liquid crystal display panel.

FIG. 3 is a diagram schematically showing a unit pixel of a firststructural example.

FIG. 4 is a diagram schematically showing an example of a display areain which unit pixels of the first structural example are arranged.

FIG. 5 is a diagram schematically showing a unit pixel of a secondstructural example.

FIG. 6 is a diagram schematically showing an example of a display areain which unit pixels of the second structural example are arranged.

FIG. 7 is a diagram schematically showing a unit pixel of a thirdstructural example.

FIG. 8 is a diagram schematically showing an example of a display areain which unit pixels of the third structural example are arranged.

FIG. 9 is a diagram schematically showing a unit pixel of a fourthstructural example.

FIG. 10 is a diagram schematically showing an example of a display areain which unit pixels of the fourth structural example are arranged.

FIG. 11 is a diagram showing an example of moiré produced byinterference between a prism sheet and a display area.

FIG. 12 is a diagram schematically showing a first prism sheet in whichprisms are arranged, and a display area in which unit pixels arearranged, according to the first embodiment.

FIG. 13 is a diagram illustrating an example of a procedure whichdetermines the angle of inclination of the prisms according to the firstembodiment.

FIG. 14 is a diagram schematically showing a first prism sheet in whichprisms are arranged, and a display area in which unit pixels arearranged, according to the second embodiment.

FIG. 15 is a diagram illustrating an example of a procedure whichdetermines the prism pitch according to the second embodiment.

FIG. 16 is a diagram schematically showing a second prism sheet in whichprisms are arranged, and a display area in which unit pixels arearranged, according to the second embodiment.

DETAILED DESCRIPTION

Generally, according to one embodiment, a display device comprises adisplay panel, a light source, a light guide and a prism sheet. Thedisplay panel includes a display area in which unit pixels are arrangedalong a first direction and a second direction intersecting the firstdirection, each unit pixel comprising a plurality of types of sub-pixelsincluding at least one first sub-pixel displaying a first color and atleast one second sub-pixel displaying a second color different from thefirst color, the first sub-pixel having a width different from that ofthe second sub-pixel in at least one of the first direction and thesecond direction, or each pixel containing different numbers of firstsub-pixels and second sub-pixels. The light guide comprises an endportion opposing the light source. The prism sheet is interposed betweenthe light guide and the display panel and comprises a plurality ofprisms extending along a third direction inclined with respect to thesecond direction by an acute angle of inclination.

According to another embodiment, when the prism pitch by which aluminance distribution of the sub-pixels in the display area is in amost uniform state is defined as an ideal pitch, each of the pluralityof types of sub-pixels has a specific ideal pitch, and the prism pitchis an average of the ideal pitches of at least two of the plurality oftypes of sub-pixels.

Embodiments will now be described with reference to accompanyingdrawings.

Note that the disclosure is presented for the sake of exemplification,and any modification and variation conceived within the scope and spiritof the invention by a person having ordinary skill in the art arenaturally encompassed in the scope of invention of the presentapplication. Furthermore, a width, thickness, shape, and the like ofeach element are depicted schematically in the figures as compared toactual embodiments for the sake of simpler explanation, and they do notlimit the interpretation of the invention of the present application.Furthermore, in the description and Figures of the present application,structural elements having the same or similar functions will bereferred to by the same reference numbers and detailed explanations ofthem that are considered redundant may be omitted.

In this embodiment, a liquid crystal display device is disclosed as anexample of the display device. This liquid crystal display device can beused in various devices such as smartphone, tablet, mobile phone,notebook computer, and game console.

FIG. 1 is a cross-sectional view schematically showing an example of thestructure of a liquid crystal display device 1. The liquid crystaldisplay device 1 includes, for example, a backlight BL and a liquidcrystal display panel LPN disposed on the backlight BL.

The backlight BL includes a light source 10 and a light guide 11.Further, the backlight BL includes a reflector 12 disposed in a firstmain surface 11A side of the light guide 11, a scattering sheet 13disposed in a second main surface 11B side of the light guide 11, afirst prism sheet 14 and a second prism sheet 15. The light guide 11,the scattering sheet 13, the first prism sheet 14 and the second prismsheet 15 have, for example, a rectangular shape of substantially thesame dimensions, and these members are stacked mutually one anothertightly in this order. The second prism sheet 15 opposes the liquidcrystal display panel LPN.

The light source 10 comprises a number of point light sources arrangedin a straight line, for example, at one end of the light guide 11. Thepoint light sources are, for example, light-emitting diodes (LEDs) ororganic electroluminescent elements (organic EL). The light source 10may be a linear light source which employs a cold cathode fluorescencetube or a hot cathode fluorescent tube.

The light guide 11 receives light from the light source 10 and outputsuniform light from the second main surface 11B towards the scatteringsheet 13. The reflector 12 reflects the light emitted from the firstmain surface 11A of the light guide 11 and returns it to the light guide11.

The scattering sheet 13 diffuses the light from the second main surface11B of the light guide 11 so that the luminance of light which entersthe first prism sheet 14 becomes uniform. As the scattering sheet 13,for example, a type which has an irregular configuration which diffuseslight on the surface or a type which contains fine particles or thelike, which has a refractive index different from that of the basematerial can be used.

The first prism sheet 14 comprises a large number of prisms 14 a eachhaving, for example, a uniform sectional shape and extending linearly.The prisms 14 a are formed on a side of the sheet 14, which opposes thesecond prism sheet 15. The second prism sheet 15 comprises a largenumber of prisms 15 a each having, for example, a uniform sectionalshape and extending linearly. The prisms 15 a are formed on a side ofthe sheet 15, which opposes the liquid crystal display panel LPN. Thesectional shape of each of prisms 14 a and 15 a is, for example, atriangle whose vertex angle is about 90 degrees. Each of prism 14 a and15 a concentrates the spread angle of the light diffused by thescattering sheet 13 within a predetermined angle range. The first prismsheet 14 and the second prism sheet 15 are arranged so that, forexample, prisms 14 a and 15 a extend in directions which intersect oneanother, for example, perpendicularly (directions in which ridgelinesthereof extend).

FIG. 2 is a sectional view schematically showing an example of thestructure of the liquid crystal display panel LPN. The liquid crystaldisplay panel LPN includes a display area DA configured to displayimages. A unit pixel PX achieving color display contains a plurality ofkinds of sub-pixels corresponding to different colors, respectively. Theunit pixel PX is the minimum unit which constitutes a color imagedisplayed on the display area DA. The example of FIG. 2 shows astructure of unit pixel PX in which sub-pixels PXR, PXG, PXB and PXW,respectively corresponding to red, green, blue and white are aligned ina first direction X.

The liquid crystal display panel LPN comprises an array substrate AR, acounter-substrate CT disposed to oppose the array substrate AR, and aliquid crystal layer LQ held between the array substrate AR and thecounter-substrate CT.

The array substrate AR comprises a first insulating substrate 20 of aglass substrate, a resin substrate or the like, that has a lighttransmissivity, a first insulating layer 21 to cover an inner surface (,which is on the counter-substrate CT side) of the first insulatingsubstrate 20, a common electrode CE disposed on the first insulatinglayer 21 and a second insulating layer 22 configured to cover the commonelectrode CE.

Further, the array substrate AR comprises pixel electrodes PER, PEG, PEBand PEW respectively corresponding to the sub-pixels PXR, PXG, PXB andPXW, and a first alignment film AL1 which covers the pixel electrodesPER, PEG, PEB and PEW and the second insulating layer 22 and is incontact with the liquid crystal layer LQ. The common electrode CE andthe pixel electrodes PER, PEG, PEB and PEW oppose each other via thesecond insulating layer 22. In the example of FIG. 2, the pixelelectrodes PER, PEG, PEB and PEW each comprising a plurality of slitsPSL. The common electrode CE and the pixel electrodes

PER, PEG, PEB and PEW are formed of, for example, a transparentconductive material such as indium tin oxide (ITO) or indium zinc oxide(IZO).

The counter-substrate CT comprises a second insulating substrate 30 of aglass substrate or a resin substrate, that has a light transmissivityand color filters CFR, CFG, CFB and CFW and a black matrix 31 providedon an inner surface (, which is on the array substrate AR side) of thesecond insulating substrate 30.

The color filter CFR is formed of a resin material colored red, forexample and is arranged in the red sub-pixel PXR. The color filter CFGis formed of a resin material colored green, for example and is arrangedin the green sub-pixel PXG. The color filter

CFB is formed of a resin material colored blue, for example and isarranged in the blue sub-pixel PXB. The color filter CFW is formed of aresin material colored white, for example and is arranged in the whitesub-pixel PXW. Note that the color filter CFW may not be formed of atransparent resin material, or the white sub-pixel PXW may not beprovided with the color filter CFW.

The black matrix 31 is configured to separate the sub-pixel PXR, PXG,PXB and PXW from each other for compartmentalization. The boundaries ofthe color filters CFR, CFG, CFB and CFW are located above the blackmatrix 31.

The counter-substrate CT further comprises an overcoat layer 33 whichcovers the color filters CFR, CFG, CFB and CFW and the black matrix 31,and a second alignment film AL2 which covers the overcoat layer 33 andis in contact with the liquid crystal layer LQ. The overcoat layer 33 isformed, for example, of a transparent resin material.

On an outer surface (, which is on the backlight BL side) of the firstinsulating substrate 20, a first optical device OD1 containing a firstpolarizer PL1 is provided. On an outer surface (, which is on anopposite side to the array substrate AR), a second optical device OD2containing a second polarizer PL2 is provided. The first polarizationaxis (or the first absorption axis) of first polarizer PL1 and thesecond polarization axis (or the second absorption axis) of secondpolarizer PL2 are situated to be, for example, perpendicular to eachother in a crossed Nicol relationship.

Note that the structure shown in FIG. 2 is applicable to, as an example,a liquid crystal display panel LPN of a mode which utilizes lateralelectric fields (including fringe electric field) for switching liquidcrystal molecules. Note that the mode of the liquid crystal displaypanel LPN is not restricted to that utilizing lateral electric fields,but may be that utilizes vertical electric fields for switching ofliquid crystal molecules such as a twisted nematic (TN) mode orvertically aligned (VA) mode.

In this embodiment, at least some of those types of sub-pixels differfrom the others in shape or the number contained in a unit pixel PX.Here, the difference in the shape of a sub-pixel refers to that thewidth of the sub-pixel in at least one of the first direction X and thesecond direction Y perpendicular to the first direction X differs.Examples of the structures of such a unit pixel PX and display area DAwill now be described with reference to FIGS. 3 to 10.

In each structural example, the unit pixel PX comprises red, green, blueand white sub-pixels PXR, PXG, PXB and PXW. Note that the unit pixel PXneed not to include one or more of these sub-pixels, or may include asub-pixel(s) of other color(s), for example, yellow in place thereof orin addition thereto.

Further, in each example, the widths of the sub-pixels PXR, PXG, PXB andPXW in the first direction X are defined as W_(RX), W_(GX), W_(BX), andW_(WX), respectively, and the widths of the sub-pixels PXR, PXG, PXB andPXW in the second direction Y are defined as W_(RY), W_(GY), W_(BY), andW_(WY), respectively. The display area DA comprises a plurality of unitpixels PX arranged in the first direction X and the second direction Y.

(First Structural Example)

FIG. 3 schematically shows a unit pixel PX according to the firststructural example. In this unit pixel PX, sub-pixels PXR, PXG, PXB andPXW are arranged in the first direction X in this order.

The width W_(GX) of the sub-pixel PXG in the first direction X is lessthan the width W_(RX) of the sub-pixel PXR in the first direction X(W_(GX)<W_(RX)). The width W_(BX) of the sub-pixel PXB in the firstdirection X is greater than the width W_(RX) of the sub-pixel PXR in thefirst direction X (W_(BX)>W_(RX)). The width W_(WX) of the sub-pixel PXWin the first direction X is equal to the width W_(RX) of the sub-pixelPXR in the first direction X (W_(WX)=W_(RX)).

The widths W_(RY), W_(GY), W_(BY), and W_(WY) of the sub-pixels PXR,PXG, PXB and PXW in the second direction Y are equal(W_(RY)=W_(GY)=W_(BY)=W_(WY)).

FIG. 4 schematically shows an example of display area DA in which unitpixels PX of the first structural example are arranged. This figureillustrates only a part of the display area DA. In the display area DA,unit pixels PX are arranged along the first direction X and the seconddirection Y so that the sub-pixels PXR, PXG, PXB and PXW are all locatedsequentially in the second direction Y.

(Second Structural Example)

FIG. 5 schematically shows a unit pixel PX according to the secondstructural example. In this unit pixel PX, two sub-pixels PXR of thesame size are arranged in the second direction Y. In the first directionX, sub-pixels PXB and PXW are arranged in the second direction Y next tothe two sub-pixels PXG, respectively.

The widths W_(RX), W_(GX), W_(BX), and W_(WX) of the sub-pixels PXR,PXG, PXB and PXW in the first direction X are equal(W_(RX)=W_(GX)=W_(BX)=W_(WX)). The widths W_(RY), W_(GY), W_(BY), andW_(WY) of the sub-pixels PXR, PXG, PXB and PXW in the second direction Yare equal (W_(RY)=W_(GY)=W_(BY)=W_(WY)).

FIG. 6 schematically shows an example of display area DA in which unitpixels PX of the second structural example are arranged. This figureillustrates only a part of the display area DA. In the display area DA,unit pixels PX are arranged along the first direction X and the seconddirection Y so that the sub-pixels PXR and PXG are both locatedsequentially in the second direction Y. In two unit pixels PX next toeach other in the first direction X, the locations of the sub-pixel PXBand PXW are replaced with each other.

(Third Structural Example)

FIG. 7 schematically shows a unit pixel PX according to the thirdstructural example. In this unit pixel PX, the locations of sub-pixelsPXR, PXG, PXB and PXW are the same as those of the second structuralexample.

The width W_(GX) of the sub-pixel PXG in the first direction X is equalto the width W_(RX) of the sub-pixel PXR in the first direction X(W_(GX)=W_(RX)). The width W_(BX) of the sub-pixel PXB in the firstdirection X is equal to the width W_(WX) of the sub-pixel PXW in thefirst direction X, and also they are greater than the width W_(RX) ofthe sub-pixel PXR in the first direction X (W_(BX)=W_(WX)>W_(RX)).

The widths W_(RY), W_(GY), W_(BY), and W_(WY) of the sub-pixels PXR,PXG, PXB and PXW in the second direction Y are equal(W_(RY)=W_(GY)=W_(BY)=W_(WY)).

FIG. 8 schematically shows an example of display area DA in which unitpixels PX of the third structural example are arranged. This figureillustrates only a part of the display area DA. In the display area DA,unit pixels PX are arranged along the first direction X and the seconddirection Y so that the sub-pixels PXR and PXG are both locatedsequentially in the second direction Y. As in the second structuralexample, in two unit pixels PX next to each other in the first directionX, the locations of the sub-pixel PXB and PXW are replaced with eachother.

(Fourth Structural Example)

FIG. 9 schematically shows a unit pixel PX according to the fourthstructural example. In this unit pixel PX, two sub-pixels PXR of thesame size and two sub-pixels PXG of the same size are arrangedalternately in the second direction Y. In the first direction X,sub-pixels PXB and PXW are arranged in the second direction Y next tothe two sub-pixels PXR and the two sub-pixels PXG, respectively.

The widths W_(RX), W_(GX), W_(BX), and W_(WX) of the sub-pixels PXR,PXG, PXB and PXW in the first direction X are equal(W_(RX)=W_(GX)=W_(BX)=W_(WX)).

The widths W_(RY) and W_(GY) of the sub-pixels PXR and PXG in the seconddirection Y are equal (W_(RY)=W_(GY)). The widths W_(BY) and W_(WY) ofthe sub-pixels PXB and PXW in the second direction Y are equal and abouttwice the width W_(RY) (W_(BY)=W_(WY)=2W_(RY)).

FIG. 10 schematically shows an example of display area DA in which unitpixels PX of the fourth structural example are arranged. This figureillustrates only a part of the display area DA. In the display area DA,unit pixels PX are arranged along the first direction X and the seconddirection Y. As in the second and third structural examples, in two unitpixels PX next to each other in the first direction X, the upper andlower locations of the sub-pixel PXB and PXW are replaced with eachother.

Subsequently, an example of the moiré resulting from a prism sheet and adisplay area in a general liquid crystal display will now be describedusing FIG. 11.

When light from the light source passes through the prism sheet in whichprisms are arranged at equal pitches, for example, stripe pattern S1 ofa high-luminance part and a low-luminance part repeating alternately asshown in FIG. 11 (a) is produced. The low-luminance parts are indicatedby solid lines and the high-luminance parts are regions between solidlines in the figure. The pitch of pattern S1 coincides with the pitch ofthe prisms. Further, when light from the light source passes through thedisplay area where a group of sub-pixels of a certain color, linearlyaligned in the first direction, are arranged with gaps therebetween atequal pitches in the second direction perpendicular to the firstdirection, stripe pattern S2 of a high-luminance part and alow-luminance part repeating alternately as shown in FIG. 11 (b) isproduced. The pitch of pattern S2 coincides with the pitch of thesub-pixels in the second direction (the distance between two sub-pixelsnext to each other in the second direction).

When the display area is viewed from outside, pattern S3 in whichpatterns S1 and S2 overlaying one another as shown in FIG. 11 (c) isproduced. In pattern S3, areas where low-luminance parts of patterns S1and S2 overlay show a high luminance, and areas where low-luminanceparts of patterns S1 and S2 do not overlap show a low luminance.Generally, the repetition cycle of the high-luminance part and thelow-luminance part in patterns S1 and S2 is extremely short, thepatterns S1 and S2 are hard to recognize by the naked eye. On the otherhand, the repetition cycle in pattern S3 is longer than those of thepatterns S1 and S2, the periodic repetition of the difference inluminance in pattern S3 is recognized as moiré when viewed.

Note that the moiré produced when the high-luminance parts and thelow-luminance parts in patterns S1 and S2 are all parallel to each otheris explained above with reference to FIG. 11. However, even if thehigh-luminance parts and the low-luminance parts in patterns S1 and S2cross by an angle each other, the high-luminance parts and thelow-luminance parts appear in pattern S3 and they can be recognized asmoiré when viewed.

FIG. 12 illustrates an example of the method of suppressing such a moiréas described above. Here, a moiré resulting from the first prism sheet14 is focused, and the first prism sheet 14 in which prisms 14 a arearranged and the display area DA in which unit pixels PX are arrangedare schematically shown. Prisms 14 a are each extending linearly alongfirst extending direction D1 (third direction) and arranged at firstprism pitch P₁ parallel to each other along second extending directionD2 perpendicular to first extending direction D1.

First extending direction D1 of prisms 14 a are inclined by an angle θ,which is an acute angle with respect to the second direction Y(0°<θ<90°). Here, since the first direction X is perpendicular to thesecond direction Y, first extending direction D1 is inclined by an acuteangle of θ with respect to the first direction X as well (90°−θ).

Note that prisms 15 a of the second prism sheet 15 extend along secondextending direction D2. That is, second extending direction D2 areinclined with respect to the second direction Y by an acute angle(90°−θ). Further, since the first direction X is perpendicular to thesecond direction Y, second extending direction D2 is inclined withrespect to the first direction X as well by an acute angle (θ).

The moiré which might have resulted from prisms of prism sheets andvarious types of sub-pixels can be suppressed by inclining the extendingdirection of the prisms with respect to the display area DA at an idealangle φ specifically for each of these various sub-pixels. The idealangle φ is an angle by which, for example, the luminancees of sub-pixelsare made most uniform in the display area DA as a whole.

Ideal angles φ for the sub-pixels are substantially equal if the shapesand the number of the various sub-pixels contained in unit pixels arethe same. Therefore, moiré can be inhibited by setting this angle to anangle of inclination θ.

On the other hand, when at least some of sub-pixels PXR, PXG, PXB andPXW differ in shape from each other in each unit pixel PX or the numberof sub-pixels of one type is different from the number of those ofanother type in each unit pixel PX as in the first to fourth structuralexamples, ideal angles φ of the sub-pixels do not become the same. Inthis case, the ideal angle φ of the sub-pixels should be determined.FIG. 13 shows an example of such a procedure of determining the idealangle.

[Procedure 1]

First, the first sub-pixel having the highest luminance and the secondsub-pixel having the second highest luminance are selected from thevarious types of sub-pixels PXR PXG, PXB and PXW. Then, first idealangle φ₁, which is an ideal angle φ specific to the first sub-pixel andsecond ideal angle φ₂, which is an ideal angle φ specific to the secondsub-pixel are determined. FIG. 13 shows an example in which first idealangle φ₁ is less than second ideal angle φ₂, but, in some other cases,first ideal angle φ₁ may be greater than second ideal angle φ₂.

Ideal angles φ₁ and φ₂ can be determined, for example, by simulationusing a computer. In this simulation, for example, a first model of thepattern produced in the light which passed prisms 14 a, and a secondmodel of the pattern produced in the light which passed the display areaDA in which only one type of the first sub-pixels and the secondsub-pixels to be subjected to operation are arranged while beingsuperimposed one on another on a virtual plane. Then, the degree ofoccurrence of moiré (that is, the presence/absence or strength of moiré,etc) is evaluated by changing the angle made between the first model andsecond model. The evaluation may be carried out by the naked eye whiledisplaying the first model and second model on the screen, or bycalculation of the luminance distribution appearing on the overlaidfirst model and second model. In such an evaluation, the angle (angle bywhich luminance distribution is made most uniform) by which moiré isinhibited most is defined as the ideal angle φ for the sub-pixelsubjected to operation. By carrying out such a simulation and evaluationfor both the first sub-pixel and second sub-pixel, ideal angles φ₁ andφ₂ can be determined.

[Procedure 2]

Then, the angle of inclination θ is determined based on each of idealangles φ₁ and φ₂ determined in Procedure 1. The angle of inclination θcan be defined, for example, between ideal angles φ₁ and φ₂ (φ₁<θ<φ₂ orφ₂<θ<φ₁).

Near first ideal angle φ₁, the moiré produced by interference betweenthe first sub-pixel and prisms 14 a is suppressed further as the angleof inclination θ becomes closer to the first ideal angle φ₁. Similarly,near second ideal angle φ₂, the moiré produced by interference betweenthe second sub-pixel and prisms 14 a is suppressed further as the angleof inclination θ becomes closer to the second ideal angle φ₂.

Therefore, if the angle of inclination θ is defined between ideal anglesφ₁ and φ₂, the moiré produced by interference between prisms 14 a andthe display area DA is suppressed on the whole as compared to the casewhere the angle of inclination θ is defined outside this range.

In addition, as the luminance of the sub-pixel is higher, thenoticeability of moiré produced by interference between the sub-pixeland prism 14 a becomes high. Therefore, by determining the angle ofinclination θ using the ideal angles φ₁ and φ₂ for the first sub-pixeland the second sub-pixel, which have high luminance, it becomes possibleto effectively suppress the occurrence of highly noticeable moirés.

As an example, the angle of inclination θ can be obtained by simplyaveraging the ideal angles φ₁ and φ₂ as indicated in the followingEquation (1).θ=(φ₁+φ₂)/2  (1)

As another example, the angle of inclination θ can be obtained byweighted average of the ideal angles φ₁ and φ₂ as indicated in thefollowing Equation (2).θ(B ₁·φ₁ +B ₂·φ₂)/(B ₁ +B ₂)  (2)

In this Equation, B₁ represents the luminance of the first sub-pixel(the first luminance) and B₂ represents the luminance of the secondsub-pixel (the second luminance). With use of the weighted averageaccording to luminance, the angle of inclination θ can be determined tobe close to the ideal angle φ of a sub-pixel with a highly noticeablemoiré (sub-pixel with high luminance) and thus the moiré which mighthave resulted from the sub-pixel can be suppressed with priority.

The weighted average may be carried out using coefficient C₁ (firstcoefficient) and coefficient C₂ (second coefficient) other than theluminance B₁ or B₂ as in the Equation (3) below. As the coefficient C1,various parameters regarding the first sub-pixel can be used, apart fromthe luminance B₁, for example, the width of the first sub-pixel in thefirst direction X or second direction Y, or the number of the firstsub-pixels contained in the unit pixel PX. As the coefficient C₂,various parameters regarding the second sub-pixel can be used, apartfrom the luminance B₂, for example, the width of the second sub-pixel inthe first direction X or second direction Y, or the number of the secondsub-pixels contained in the unit pixel PX.θ=(C ₁·φ₁ +C ₂·φ₂)/(C ₁ +C ₂)  (3)

The weighted average may be carried out using the values obtained bymultiplying coefficient C₁ with luminance B₁ and coefficient C₂ withluminance B₂ as in the Equation (4) below.θ=(B ₁ ·C ₁·φ₁ +B ₂ ·C ₂ ·φ ₂)/(B ₁ ·C ₁ +B ₂ ·C ₂)  (4)

Here, an example will now be described, in which how the authors ofthese embodiments determined the angle of inclination θ. That is, as toa display area DA in which the sub-pixel PXW had the highest luminanceand the sub-pixel PXG had the second highest luminance, the angle ofinclination θ was determined using the Equation (2) above. Then, themoiré resulting from the first prism sheet 14 in which the firstextending direction D1 of prisms 14 a were inclined with respect to thesecond direction Y by the determined angle, and the display area DA, wasevaluated.

The ratio of the luminance B₁ of the sub-pixel PXW which is the firstsub-pixel and the luminance B₂ of the sub-pixel PXG which is the secondsub-pixel is expressed as: B₁:B₂=1.5:1. In Procedure 1 described above,the first ideal angle φ₁ of the sub-pixel PXW and the second ideal angleφ₂ of the sub-pixel PXG were obtained by simulation, and the first idealangle φ₁ was 15° and the second ideal angle φ₂ was 28°.

In this case, by the Equation (2) provided above,θ=(1.5·15°+1.28°)/(1.5+1)≈20° is obtained. When the first extendingdirection D1 of prisms 14 a was inclined with respect to the seconddirection Y by the angle of inclination θ thus obtained (=20°), moiréwas substantially not noticeable. In addition, under various conditions,the evaluation of moiré was carried out for angles of inclination θdetermined using the Equations (1) to (4). In each case, the resultindicated that the moiré was appropriately suppressed. Further, undersuch a condition that the second extending direction D2 wasperpendicular to the first extending direction D1, the moiré byinterference between prisms 15 a of the second prism sheet 15 and thedisplay area DA was also appropriately suppressed in each case.

As explained above, according to this embodiment, moiré caused byinterference between the display area DA and the first prism sheet 14 orthe second prism sheet 15 can be suppressed in the liquid crystaldisplay 1 even if at least some of sub-pixels differ in shape from eachother in each unit pixel or the number of sub-pixels of one type isdifferent from the number of those of another type in each unit pixelsPX among those arranged in the display area DA.

Note that in this embodiment, the angle of inclination θ is definedbased on the relationship between the first extending direction D1 ofprisms 14 a of the first prism sheet 14 and the second direction Y, butit is alternatively possible to define the angle of inclination θ basedon the relationship between the first extending direction D1 and thefirst direction X. Similarly, the angle of inclination θ may be definedbased on the relationship between the second extending direction D2 ofprisms 15 a of the second prism sheet 15 and the first direction X1 orsecond direction Y.

Further, in this embodiment, the angle of inclination θ is determinedusing the first ideal angle φ1 of the first sub-pixel with the highestluminance and the second ideal angle φ2 of the second sub-pixel with thesecond highest luminance. But it is also possible to determine the angleof inclination θ using ideal angles φ of more sub-pixels. In otherwords, assuming that unit pixels PX each comprise n-types (n>=2) ofsub-pixels, the angle of inclination θ can be determined based on theideal angles φ of 2 or more but n or less types of sub-pixels.

For example, the angle of inclination θ may be determined using, inaddition to the first sub-pixel and the second sub-pixel, the thirdideal angle φ3 of the third sub-pixel having the third highest luminanceamong the sub-pixels of each unit pixel PX. In this case, the followingEquations (5) to (8) can be used in place of the Equation (1) to (4)provided above.θ=(φ₁+φ₂+φ₂)/3  (5)θ=(B ₁·φ₁ +B ₂·φ₂ +B ₃·φ₃)/(B₁ +B ₂ +B ₃)   (6)θ=(C ₁·φ₁ +C ₂·φ₂ +C ₃·φ₃)/(C ₁ +C ₂ +C ₃)  (7)θ=(B ₁ ·C ₁·φ₁ +B ₂ ·C ₂·φ₂ +B ₃ ·C ₃ ·φ ₃)/(B₁ ·C ₁ +B ₂ ·C ₂ +B ₃ ·C₃)  (8)

In these Equations, B₃ represents the luminance of the third sub-pixel(the third luminance) and C₃ represents a coefficient different fromluminance B₃ (the third coefficient). As coefficient C₃, variousparameters regarding the third sub-pixel, apart from the luminance B₃,for example, the width of the third sub-pixels in the first direction Xor the second direction Y or the number of the third sub-pixelscontained in unit pixel PX, can be used.

As described above, even if the angle of inclination θ is determined inconsideration of ideal angles φ of three or more types of sub-pixels,the moiré which might have resulted from the first prism sheet 14 orsecond prism sheet 15 and the display area DA can be suppressed.

(Second Embodiment)

The second embodiment will now be described. This embodiment disclosesother methods of reducing or preventing the moiré produced byinterference between the display area DA and the first prism sheet 14 orsecond prism sheet 15. The structures, operations and the like of thisembodiment are similar to those of the first embodiment unlessparticularly referred to.

FIG. 14 schematically shows a first prism sheet 14 in which prisms 14 aare arranged and a display area DA in which unit pixels PX are arranged.Prisms 14 a are each extending linearly along third extending directionD1 (third direction) and arranged at first prism pitch P₁ parallel toeach other. In the example of FIG. 14, the first extending direction D1is the same as the second direction Y. That is, the angle of inclinationθis 0°.

The moiré which might have resulted from interference between prisms 14a of the first prism sheet 14 and various types of sub-pixels containedin unit pixels PX can be suppressed by arranging prisms 14 a at idealpitches Q each specific to each respective sub-pixel. The ideal pitchesQ are, for example, those which make the luminances of sub-pixels mostuniform in the display area DA on the whole.

The ideal pitches Q become equal among various types of sub-pixels ifthe sub-pixels contained in unit pixels PX are the same in shape and thesame number of sub-pixels are contained in each unit pixel PX.Therefore, the moiré can be suppressed by setting this pitch to thefirst prism pitch P₁.

Note that the ideal pitch Q for the case where various types ofsub-pixels contained in unit pixels PX are the same in shape and thesame number of sub-pixels are contained in each unit pixel PX will be avalue obtained by multiplying the width of the sub-pixels with a naturalnumber, or dividing it a natural number. This is because if the idealpitch Q takes such a value, the spatial relationships between the shadeof each prism 14 a and each respective sub-pixel are made uniform on thescreen on the whole and luminance distribution is equalized.

On the other hand, when at least some of sub-pixels PXR, PXG, PXB andPXW differ in shape from each other in each unit pixel PX or the numberof sub-pixels of one type is different from the number of those ofanother type in each unit pixels PX as in the first to fourth structuralexamples, ideal pitches Q of the sub-pixels do not become the same. Inthis case, the first prism pitch P₁ should be determined. FIG. 15 showsan example of such a procedure of determining the first prism pitch P₁.

[Procedure 1]

First, the first sub-pixel having the highest luminance and the secondsub-pixel having the second highest luminance are selected from thevarious types of sub-pixels PXR PXG, PXB and PXW. Then, first idealpitch Q₁, which is an ideal pitch Q for the first sub-pixel and secondideal pitch Q₂, which is an ideal pitch Q for the second sub-pixel aredetermined. FIG. 15 shows an example in which first ideal pitch Q₁ isless than second ideal pitch Q₂, but, in some other cases, first idealpitch Q₁ may be greater than second ideal pitch Q₂.

Ideal pitch Q₁ and Q₂ can be determined, for example, by computersimulation. In this simulation, for example, a first model of thepattern produced in the light which passed prisms 14 a, and a secondmodel of the pattern produced in the light which passed the display areaDA in which only one type of the first sub-pixels and the secondsub-pixels to be subjected to operation are arranged while superimposedone on another on a virtual plane. Then, the degree of occurrence ofmoiré (that is, the presence/absence or strength of moiré, etc) isevaluated by changing the first prism pitch P₁. The evaluation may becarried out by the naked eye while displaying the first model and secondmodel on the screen, or by calculation of the luminance distributionappearing on the overlaid first model and second model. In such anevaluation, the pitch of prism 14 a by which moiré is inhibited most(pitch by which luminance distribution is made most uniform) is definedas the ideal pitch Q for the sub-pixel subjected to operation. Bycarrying out such a simulation and evaluation for both the firstsub-pixel and second sub-pixel, ideal pitches Q₁ and Q₂ can bedetermined.

[Procedure 2]

Then, the first prism pitch P₁ is determined based on each of idealpitches Q₁ and Q₂ determined in Procedure 1. The first prism pitch P₁can be defined, for example, between ideal pitches Q₁ and Q₂ (Q₁<P₁<Q₂or Q₂<P₁<Q₁).

Near first ideal pitch Q₁, the moiré produced by interference betweenthe first sub-pixel and prisms 14 a is suppressed further as the firstprism pitch P₁ becomes closer to the first ideal pitches Q₁. Similarly,near second ideal pitch Q₂, the moiré produced by interference betweenthe second sub-pixel and prisms 14 a is suppressed further as the firstprism pitch P₁ becomes closer to the second ideal pitch Q₂. Therefore,if the first prism pitch P₁ is defined between ideal pitches Q₁ and Q₂,the moiré produced by interference between prisms 14 a and the displayarea DA is suppressed on the whole as compared to the case where thefirst prism pitch P₁ is defined outside this range.

In addition, as the luminance of the sub-pixel is higher, thenoticeability of moiré produced by interference between the sub-pixeland prism 14 a becomes high. Therefore, by determining the first prismpitch P₁ using the ideal pitches Q₁ and Q₂ for the first sub-pixel andthe second sub-pixel, which have high luminance, it becomes possible toeffectively suppress the occurrence of highly noticeable moirés.

As an example, the first prism pitch P₁ can be obtained by simplyaveraging the ideal pitches Q₁ and Q₂ as indicated in the followingEquation (9).P ₁=(Q ₁ +Q ₂)/2  (9)

As another example, the first prism pitch P₁ can be obtained by weightedaverage using luminance B₁ of the first sub-pixel (the first luminance)and luminance B₂ of the second sub-pixel (the second luminance) asindicated in the following Equation (10). With use of the weightedaverage according to luminance, the first prism pitch P₁ can bedetermined to be closer to the ideal pitch Q of a sub-pixel with ahighly noticeable moiré (sub-pixel with high luminance) and thus themoiré which might have resulted from the sub-pixel can be suppressedwith priority.P ₁=(B ₁·Q₁ +B ₂ ·Q ₂)/(B ₁ +B ₂)  (10)

The weighted average may be carried out using coefficient C₁ (firstcoefficient) and coefficient C₂ (second coefficient) other than theluminance B₁ or B₂ as in the Equation (11) below. As the coefficient C1,various parameters regarding the first sub-pixel can be used, apart fromthe luminance B₁. Examples of these parameters are the width of thefirst sub-pixel in the first direction X or second direction Y, and thenumber of the first sub-pixels contained in the unit pixel PX. As thecoefficient C₂, various parameters regarding the second sub-pixel can beused, apart from the luminance B₂. Examples of these parameters are thewidth of the second sub-pixel in the first direction X or seconddirection Y, and the number of the second sub-pixels contained in theunit pixel PX.P ₁=(C ₁ ·Q ₁ +C ₂ ·Q ₂)/(C ₁ +C ₂)  (11)

The weighted average may be carried out using the values obtained bymultiplying coefficient C₁ with luminance B₁ and coefficient C₂ withluminance B₂ as in the Equation (12) below.P ₁=(B ₁ ·C ₁ ·Q ₁ +B ₂ ·C ₂ ·Q ₂)/(B ₁ ·C ₁ +B ₂ ·C ₂)  (12)

Here, an example how to determine the first prism Pitch P₁ will bedescribed below. That is, as to a display area DA in which the sub-pixelPXW had the highest luminance and the sub-pixel PXG had the secondhighest luminance, the first prism pitch P₁ was determined using theEquation (10) above. Then, the moiré, resulting from the first prismsheet 14 in which prisms 14 a are arranged at this pitch and the displayarea DA, was evaluated.

The ratio of the luminance B₁ of the sub-pixel PXW which is the firstsub-pixel and the luminance B₂ of the sub-pixel PXG which is the secondsub-pixel is expressed as: B₁:B₂=1.5:1. In Procedure 1 described above,the ideal pitch Q₁ of the sub-pixel PXW and the ideal pitch Q₂ of thesub-pixel PXG by were obtained by simulation, and the first ideal pitchQ₁ was 30 μm and the second ideal pitch Q₂ was 15 μm.

In this case, by the Equation (10) provided above,P₁=(1.5·30+1·15)/(1.5+1)=24 μm is obtained. When the first prism sheet14 in which prisms 14 a were arranged at the first prism pitch P₁ thusdetermined (=24 μm) was used, moiré was substantially not noticeable. Inaddition, under various conditions, the evaluation of moiré was carriedout for first prism pitches P₁ determined using the Equations (9) to(12). In each case, the result indicated that the moiré wasappropriately suppressed.

Note that in this embodiment, the first prism pitch P₁ is determinedusing the first ideal pitch Q₁ of the first sub-pixel with the highestluminance and the second ideal pitch Q2 of the second sub-pixel with thesecond highest luminance. But it is also possible to determine the firstprism pitch P₁ using ideal pitches Q of more sub-pixels. In other words,assuming that unit pixels PX each comprise n-types (n>=2) of sub-pixels,the first prism pitch P₁ can be determined based on the ideal pitches Qof 2 or more but n or less types of sub-pixels.

For example, the first prism pitch P₁ may be determined using, inaddition to the first sub-pixel and the second sub-pixel, the thirdideal pitch Q₃ of the third sub-pixel having the third highest luminanceamong the sub-pixels of each unit pixel PX. In this case, the followingEquations (13) to (16) can be used in place of the Equation (9) to (12)provided above.P ₁=(Q ₁ +Q ₂ +Q ₂)/3  (13)P ₁=(B ₁ ·Q ₁ +B ₂ ·Q ₂ +B ₃ ·Q ₃)/(B ₁ +B ₂ +B ₃)  (14)P ₁=(C ₁ ·Q ₁ +C ₂ ·Q ₂ +C ₃ ·Q ₃)/(C ₁ +C ₂ +C ₃)  (15)P ₁=(B ₁ ·C ₁ ·Q ₁ +B ₂ ·C ₂ ·Q ₂ +B ₃ ·C ₃ ·Q ₃)/(B ₁ ·C ₁ +B ₂ ·C ₂ +B₃ ·C ₃)  (16)

In these Equations, B₃ represents the luminance of the third sub-pixel(the third luminance) and C₃ represents a coefficient different fromluminance B₃ (the third coefficient). As coefficient C₃, variousparameters regarding the third sub-pixel can be used apart from theluminance B₃. Examples of these parameters are the width of the thirdsub-pixels in the first direction X or the second direction Y and thenumber of the third sub-pixels contained in unit pixel PX.

Note that the pitch of prisms 15 a of the second prism sheet 15 can bedefined by a method similar to the above. FIG. 16 schematically showsthe second prism sheet 15 in which prisms 15 a are arranged and thedisplay area DA in which unit pixels PX ware arranged. Prisms 15 a areeach extending linearly along the second extending direction D2 andarranged at second prism pitch P₂ parallel to each other. As shown inFIG. 14, when the first extending direction D1 of prisms 14 a coincideswith the second direction Y and the first extending direction D1 isperpendicular to the second extending direction D2, the second extendingdirection D2 coincides with the first direction X.

The moiré which might have resulted from prisms 15 a and various typesof sub-pixels contained in unit pixels PX can be suppressed by arrangingprisms 15 a at ideal pitches Q each specific to each respectivesub-pixel, as in the case of prisms 14 a. The second prism pitch P₂ canbe determined by Procedures 1 and 2 similar to those of first prismpitch P₁ using ideal pitches Q for the sub-pixels of various types.

As explained above, according to this embodiment, moiré caused byinterference between the display area DA and the first prism sheet 14 orthe second prism sheet 15 can be suppressed in the liquid crystaldisplay 1 even if at least some of sub-pixels differ in shape from eachother in each unit pixel PX or the number of sub-pixels of one type isdifferent from the number of those of another type in each unit pixelsPX among those arranged in the display area DA.

Note that the structures disclosed in the first and second embodimentscan be modified into various versions when practiced. Further, regardingthe present embodiments, any advantages and effects of those obviousfrom the description of the specification or arbitrarily conceived by askilled person are naturally considered achievable by the presentinvention.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A method of suppressing moiré in a display devicecomprising: a display panel comprising a display area in which firstpixels and second pixels are arranged along a first direction and asecond direction intersecting the first direction; a light source; alight guide comprising an end portion opposing the light source; a prismsheet interposed between the light guide and the display panel andcomprising a plurality of prisms extending along a third direction,wherein each of the first pixels includes a first red sub-pixel, a firstgreen sub-pixel and a blue sub-pixel, each of the second pixels includesa second red sub-pixel, a second green sub-pixel and a white sub-pixel,the moiré being caused by interference between the prisms and thedisplay area, and the method of suppressing the moiré comprising:determining for a first sub-pixel a first ideal angle between theextending direction of the prisms and the second direction, by which aluminance distribution of the sub-pixels in the display area is in amost uniform state, the first ideal angle being specific to the firstsub-pixel having a highest luminance among the first red sub-pixel, thesecond red sub-pixel, the first green sub-pixel, the second greensub-pixel, the blue sub-pixel and the white sub-pixel; determining for asecond sub-pixel a second ideal angle between the extending direction ofthe prisms and the second direction, by which the luminance distributionof the sub-pixels in the display area is in a most uniform state, thesecond ideal angle being specific to the second sub-pixel having asecond highest luminance among the first red sub-pixel, the second redsub-pixel, the first green sub-pixel, the second green sub-pixel, theblue sub-pixel and the white sub-pixel, wherein the second ideal angleis different from the first ideal angle, and one of the first sub-pixeland the second sub-pixel is the white sub-pixel; and inclining the thirddirection with respect to the second direction by an angle ofinclination that is an average of the first ideal angle and the secondideal angle.
 2. The method of claim 1 wherein the average is a weightedaverage according to a first luminance of the first sub-pixel and asecond luminance of the second sub-pixel.
 3. The method of claim 1,wherein the average is a weighted average according to a value obtainedby multiplying the first luminance of the first sub-pixel with a firstcoefficient other than the first luminance regarding the first sub-pixeland a value obtained by multiplying the second luminance of the secondsub-pixel with a second coefficient other than the second luminanceregarding the second sub-pixel.
 4. A method of suppressing moiré in adisplay device comprising: a display panel comprising a display area inwhich first pixels and second pixels are arranged along a firstdirection and a second direction intersecting the first direction; alight source; a light guide comprising an end portion opposing the lightsource; a prism sheet interposed between the light guide and the displaypanel and comprising a plurality of prisms linearly extending, whereineach of the first pixels includes a first red sub-pixel, a first greensub-pixel and a blue sub-pixel, each of the second pixels includes asecond red sub-pixel, a second green sub-pixel and a white sub-pixel,the moiré being caused by interference between the prisms and thedisplay area, and the method of suppressing the moiré comprising:determining for a first sub-pixel a first ideal pitch between theprisms, by which a luminance distribution of the sub-pixels in thedisplay area is in a most uniform state, the first ideal pitch beingspecific to the first sub-pixel having a highest luminance among thefirst red sub-pixel, the second red sub-pixel, the first greensub-pixel, the second green sub-pixel, the blue sub-pixel and the whitesub-pixel; determining for a second sub-pixel a second ideal pitchbetween the prisms, by which the luminance distribution of thesub-pixels in the display area is in a most uniform state, the secondideal pitch being specific to the second sub-pixel having a secondhighest luminance among the first red sub-pixel, the second redsub-pixel, the first green sub-pixel, the second green sub-pixel, theblue sub-pixel and the white sub-pixel, wherein the second ideal pitchis different from the first ideal pitch, and one of the first sub-pixeland the second sub-pixel is the white sub-pixel; and arranging theprisms on the prism sheet at a prism pitch that is an average of thefirst ideal pitch and the second ideal pitch.
 5. The method of claim 4,wherein the average is a weighted average according to a first luminanceof the first sub-pixel and a second luminance of the second sub-pixel.6. The method of claim 4, wherein the average is a weighted averageaccording to a value obtained by multiplying the first luminance of thefirst sub-pixel with a first coefficient other than the first luminanceregarding the first sub-pixel and a value obtained by multiplying thesecond luminance of the second sub-pixel with a second coefficient otherthan the second luminance regarding the second sub-pixel.